[_The following passages formed part of a preface to the small
volume in which the foregoing essay re-appeared. I append them here
as they cannot now be conveniently prefixed._]
Though the direct bearings of the arguments contained in this Essay are
biological, the argument contained in its first half has indirect
bearings upon Psychology, Ethics, and Sociology. My belief in the
profound importance of these indirect bearings, was originally a chief
prompter to set forth the argument; and it now prompts me to re-issue it
in permanent form.
Though mental phenomena of many kinds, and especially of the simpler
kinds, are explicable only as resulting from the natural selection of
favourable variations; yet there are, I believe, still more numerous
mental phenomena, including all those of any considerable complexity,
which cannot be explained otherwise than as results of the inheritance
of functionally-produced modifications. What theory of psychological
evolution is espoused, thus depends on acceptance or rejection of the
doctrine that not only in the individual, but in the successions of
individuals, use and disuse of parts produce respectively increase and
decrease of them.
Of course there are involved the conceptions we form of the genesis and
nature of our higher emotions; and, by implication, the conceptions we
form of our moral intuitions. If functionally-produced modifications are
inheritable, then the mental associations habitually produced in
individuals by experiences of the relations between actions and their
consequences, pleasurable or painful, may, in the successions of
individuals, generate innate tendencies to like or dislike such actions.
But if not, the genesis of such tendencies is, as we shall see, not
satisfactorily explicable.
That our sociological beliefs must also be profoundly affected by the
conclusions we draw on this point, is obvious. If a nation is modified
_en masse_ by transmission of the effects produced on the natures of its
members by those modes of daily activity which its institutions and
circumstances involve; then we must infer that such institutions and
circumstances mould its members far more rapidly and comprehensively
than they can do if the solo cause of adaptation to them is the more
frequent survival of individuals who happen to have varied in
favourable ways.
I will add only that, considering the width and depth of the effects
which acceptance of one or other of these hypotheses must have on our
views of Life, Mind, Morals, and Politics, the question--Which of them
is true? demands, beyond all other questions whatever, the attention of
scientific men.
* * * * *
After the above articles were published, I received from Dr. Downes a
copy of a paper "On the Influence of Light on Protoplasm," written by
himself and Mr. T.P. Blunt, M.A., which was communicated to the Royal
Society in 1878. It was a continuation of a preceding paper which,
referring chiefly to _Bacteria_, contended that--
"Light is inimical to, and under favourable conditions may wholly
prevent, the development of these organisms."
This supplementary paper goes on to show that the injurious effect of
light upon protoplasm results only in presence of oxygen. Taking first a
comparatively simple type of molecule which enters into the composition
of organic matter, the authors say, after detailing experiments:--
"It was evident, therefore, that _oxygen_ was the agent of
destruction under the influence of sunlight."
And accounts of experiments upon minute organisms are followed by the
sentence--
"It seemed, therefore, that in absence of an atmosphere, light
failed entirely to produce any effect on such organisms as were
able to appear."